This invention relates generally to the field of locking systems for laundry appliance access doors. The access door of a microcontroller operated laundry appliance is manually closed to mechanically operate a line switch and to position a latch member for locking the access door closed. A solenoid is actuated by the microcontroller to lock the access door in the access-closed position and to close the contacts of a second switch for providing a door-latched signal to the microcontroller. The second switch is addressed by the microcontroller prior to locking the access door for confirming the proper operability of the second switch upon receiving the door-latched signal. The microcontroller is operable for verifying the posture of the second switch throughout preselected portions of the cycle and is operable for interrupting operation of the washing machine upon detecting an inoperable second switch or an unlocked access door.
Prior art locking systems for appliances which include rotatable members have generally utilized door locking mechanisms which provide for simply mechanically locking the access door during periods of high speed spin.
Harrold, U.S. Pat. No. 3,763,670, teaches an automatic clothes washing machine where closing of the lid moves a slide to close a first switch. Closing of the first switch conditions a solenoid circuit for actuating a locking arm into engagement with the slide for locking the lid and closing a second switch when the timer spin switch is closed. The second switch and solenoid are thus in the spin circuit of the drive motor and the lid is locked only when the washing machine is in spin and spin will proceed only when the second switch is closed.
Lay et al, U.S. Pat. No. 3,857,002, disclose appliance structure where a main switch is closed by movement of door lock structure to the locked posture. The structure includes a solenoid for moving a pin to lock the access door only when the access door is closed. If the access door is not locked the appliance will not be operable. The solenoid is connected in the control circuitry by two parallel lines, each having a switch so that one switch is closed whenever the appliance is on and the other switch is closed only when the machine is in spin. Thus, the door cannot be unlocked during spin.
The prior art does show circuitry and mechanism for locking an access door during selected periods of appliance operation, during an entire cycle of operation and for preventing operation of the appliance if the access door is not closed. There has been no known showing, however, of a microcontroller-based access door locking system for ensuring that the access door is closed and locked during predetermined portions of a cycle of operations and for ensuring that sensor switches associated with the access door are properly operable.